COVID-19 vaccines - what to expect: MedlinePlus Medical Encyclopedia (2023)

COVID-19 vaccines are used to prepare the body's immune system to protect against COVID-19. These vaccines are a vital tool to help stop the COVID-19 pandemic. Adults and children ages 6 months and older should get the COVID-19 vaccination.

Learn what to expect before and after you are vaccinated for COVID-19.


There are several ways to sign up for a vaccine:

  • Ask your doctor, pharmacist, or community health center if they provide vaccines.
  • Check your local pharmacy's website to see if vaccination appointments are available. Find out which pharmacies are participating in the Federal Retail Pharmacy Program.
  • Contact your state health department to find additional vaccination locations in the area.
  • Check the CDC VaccineFinder to find out where to get a vaccine in your area.
  • Text your ZIP code to 438829 or call 1-800-232-0233 to find vaccine locations near you in the United States.

Before you go to your appointment, check your confirmation emails to find out what you may need to bring to the appointment. For example, you may need your driver's license or other ID or proof of eligibility.

If you take any medicines, you should keep taking them as you usually do. If you take medicines that affect the immune system, talk with your health care provider to find out if getting the COVID-19 vaccine will work or cause any problems for you.

You should not take over-the-counter pain relievers such as aspirin, ibuprofen, or acetaminophen to help prevent side effects before you get the vaccine. It is not known if these medicines will affect how well the vaccine works. However, if you take these medicines regularly for other reasons, you can take them as you always do.

You should also not take antihistamines to help prevent an allergic reaction before you get the vaccine.

If you have any questions about your medicines, ask your health care provider or the vaccine provider.


You will need to wear a mask at the vaccination site the entire time. Everyone else at the site will also have to wear a mask. Try to stay at least 6 feet away from others at all times.

After you get your vaccine, you will wait at the vaccination site for 15 minutes to make sure you do not have a severe allergic reaction to the shot (this is very rare). If you have had a previous severe allergic reaction or if you have had an immediate reaction to immunizations in the past, you may need to wait for 30 minutes as a precaution. Vaccination sites are equipped to provide immediate care for severe allergic reactions and call for emergency medical care.

At your appointment, you will likely schedule the date of your second dose if you are receiving a 2-dose vaccine. You should receive a vaccination card that tells you what vaccine you received and the date and location you received it. Be sure to keep this card if needed for future use. You will need to bring it with you for your second dose if you are receiving a 2-dose vaccine.

You should contact the vaccination provider site:

  • If you did not get a vaccination card or you lose your card
  • If you did not schedule an appointment for a second dose
  • If you need to reschedule your second dose

You can also contact your state health department if you have questions about COVID-19 vaccinations.


If you got one of the 2-dose vaccines, you will need to receive your second dose within a specific number of weeks. You need to get the same type (brand) of vaccine for your second dose as you got for your first.

If you got the Pfizer-BioNTech COVID-19 vaccine, you should get your second Pfizer-BioNTech shot about 21 days (3 weeks) after the first shot.

If you got the Moderna COVID-19 vaccine, you should get your second Moderna shot about 28 days (4 weeks) after the first shot.

If you got the Novavax COVID-19 vaccine, you should get your second Novavax shot about 21 days (3 weeks) after the first shot.

The day you get your first shot, you will likely also schedule the date for your second shot.

It takes time for your immune system to start protecting you after receiving the vaccine. You are considered fully vaccinated:

  • 2 weeks after your second shot of the Pfizer-BioNTech or Moderna vaccine

You are not fully vaccinated if it has been less than 2 weeks since your second 2-dose shot. You are not fully vaccinated if you have only received 1 dose of a 2-dose vaccine.

People who have a weak immune system (immunocompromised) should get an additional dose at least 28 days after their second shot of either the Pfizer-BioNTech or Moderna mRNA vaccine. This includes people receiving certain types of cancer treatment and people taking medicines that suppress the immune system. Ask your doctor if you are not sure. Getting a third dose will improve the response to the vaccine in people with weak immune systems.


Over time, COVID-19 vaccines appear to become less protective against the virus. Getting a booster dose helps provide additional protection against COVID-19. As a result, booster shots are now recommended for all people age 5 years and older.

If you received the Pfizer-BioNTech or Moderna mRNA vaccine, you can get a booster dose 5 months after receiving your second dose of the initial vaccine.

You have the option to choose either the Pfizer-BioNTech or Moderna mRNA vaccine for your booster dose, regardless of which vaccine you first received.

If you received the Johnson and Johnson's Janssen (J&J/Janssen) vaccine you should get a booster after 2 months. In this situation, it is preferred that you receive the Pfizer-BioNTech or Moderna vaccine.

The CDC has further information about COVID-19 vaccine booster shots.


While COVID-19 vaccines will not make you sick, they may cause certain side effects and flu-like symptoms. This is normal. These symptoms are a sign that your body is making antibodies against the virus.

Common side effects include:

  • Pain, redness, and swelling on the arm where you got the shot
  • Tiredness
  • Headache
  • Muscle pain
  • Chills
  • Fever
  • Nausea

Some people get a red, itchy, swollen, painful rash in the arm where they got the shot. This is known as "COVID arm." This can occur days after getting the first shot. You should still get your second shot if you got a 2-dose vaccine. You can ask to have it in the other arm.

COVID-19 vaccines - what to expect: MedlinePlus Medical Encyclopedia (1)

To help relieve side effects, you should:

  • Move the arm where you got the shot often during the day
  • Apply a clean, cool washcloth to ease swelling and discomfort
  • Drink plenty of fluids
  • Dress lightly if you have a fever

Note that the side effects from the second dose may be more intense than those from the first shot. Symptoms from the shot may make you feel bad enough that you need to take time off from work or daily activities, but they should go away within a few days. Even if you do have side effects, it is still important to get the second shot. The risks of any side effects from the vaccine are far less dangerous than the potential for serious illness or death from COVID-19.

You may be instructed by the vaccine provider that you can take acetaminophen or another OTC medicine such as ibuprofen or aspirin to help relieve any vaccine side effects. Or, talk with your doctor about taking OTC medicine if you are not sure.

If symptoms do not go away in a few days, or if you have any concerns, you should contact your health care provider.

In rare cases, people have had severe and non-severe allergic reactions to the COVID-19 vaccines. If you have a severe or non-severe allergic reaction after getting the first shot of the COVID-19 vaccine, you should not get the second shot. Talk with your health care provider to see if there are other options.

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